[U-Boot] [PATCH v2 5/7] usb: dwc2-otg: fix warnings for ep->dma_buf for LP64 builds

[Dr. Philipp Tomsich]

> On 07 Jun 2017, at 09:53, Marek Vasut <marex at denx.de> wrote:
> 
> On 06/07/2017 09:49 AM, Dr. Philipp Tomsich wrote:
>>> On 07 Jun 2017, at 08:28, Marek Vasut <marex at denx.de
>>> <mailto:marex at denx.de>> wrote:
>>> 
>>> On 06/06/2017 05:11 PM, Dr. Philipp Tomsich wrote:
>>>> 
>>>>> On 06 Jun 2017, at 16:35, Marek Vasut <marex at denx.de
>>>>> <mailto:marex at denx.de>> wrote:
>>>>> 
>>>>> On 06/06/2017 03:42 PM, Philipp Tomsich wrote:
>>>>>> For LP64 build w/ GCC 6.3, the handling of the ep->dma_buf variable
>>>>>> when (truncating and) writing into the controller's registers is
>>>>>> unsafe and triggers the following compiler warning (thus failing by
>>>>>> buildman tests):
>>>>>> ../drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c: In function 'setdma_rx':
>>>>>> ../drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c:116:9: warning: cast
>>>>>> from pointer to integer of different size [-Wpointer-to-int-cast]
>>>>>>  writel((unsigned int) ep->dma_buf, &reg->out_endp[ep_num].doepdma);
>>>>>>         ^
>>>>>> 
>>>>>> This change fixes the warning and makes the code a bit more robust by
>>>>>> doing the following:
>>>>>> - we check whether ep->dma_buf can be safely truncated to 32 bits
>>>>>> (i.e. whether dma_buf is the same value when masked to 32 bits) and
>>>>>> emit an error message if that is not the case
>>>>>> - we cast to a uintptr_t and let the writel macro truncate the
>>>>>> uintptr_t (potentially a 64bit value) to 32bits
>>>>>> 
>>>>>> Signed-off-by: Philipp Tomsich
>>>>>> <philipp.tomsich at theobroma-systems.com
>>>>>> <mailto:philipp.tomsich at theobroma-systems.com>>
>>>>>> 
>>>>>> ---
>>>>>> 
>>>>>> Changes in v2:
>>>>>> - (new patch) fix warnings and add some robustness for the truncation
>>>>>> of ep->dma_buf in dwc2-otg for LP64 builds to fix a buildman failure
>>>>>> for u-boot-rockchip/master at 2b19b2f
>>>>>> 
>>>>>> drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c | 6 +++++-
>>>>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>> 
>>>>>> diff --git a/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>>>>>> b/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>>>>>> index 0d6d2fb..f5c926c 100644
>>>>>> --- a/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>>>>>> +++ b/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>>>>>> @@ -113,7 +113,11 @@ static int setdma_rx(struct dwc2_ep *ep,
>>>>>> struct dwc2_request *req)
>>>>>> invalidate_dcache_range((unsigned long) ep->dma_buf,
>>>>>> (unsigned long) ep->dma_buf + ep->len);
>>>>>> 
>>>>>> -writel((unsigned int) ep->dma_buf, &reg->out_endp[ep_num].doepdma);
>>>>>> +/* ensure that ep->dma_buf fits into 32 bits */
>>>>>> +if (((uintptr_t)ep->dma_buf & 0xffffffff) != (uintptr_t)ep->dma_buf)
>>>>>> +error("ep->dma_buf does not fit into a 32 bits");
>>>>> 
>>>>> You print an error, but still continue with the function ? That'll
>>>>> probably lead to a crash, you should rather abort. In fact, I suspect
>>>>> you can use bounce-buffer to assure the dma buffer is in 32bit space.
>>>> 
>>>> This tries to stay close to the current behaviour (we have no
>>>> hardware to test this,
>>>> but I wanted to get it out of the way as it caused buildman-failures)
>>>> and to provide
>>>> diagnostics for whoever first encounters an issue here.
>>>> 
>>>> Note that I would only expect a DMA error, if someone really hit this
>>>> issue ...
>>> 
>>> So this patch is just some hypothetical fix ? What triggered creation of
>>> this patch ?
>> 
>> Running buildman (w/ a GCC 6.3 configured as aarch-unknown-elf) against
>> unrelated
>> patch-series (for a Rockchip device that has a different USB controller)
>> fails due to the
>> warnings raised from this. Just casting those warnings away (without
>> having an
>> “assertion-like” diagnostic printed) doesn’t sound like the best plan
>> either, though. 
>> 
>> Details of the buildman-failure are in the above commit-message.
> 
> Ah, hm. In that case, you should really implement the bounce buffer here
> I think. Letting the transfer continue will lead to really weird
> failures and/or memory corruption.

Alright. I’ll put it to (the back of) my queue and resubmit.
Someone (with hardware) will need to test, once it’s submitted.

Cheers,
Philipp.